Magnetoresistive device and method for manufacturing same

ABSTRACT

The heat resistance of a magnetic resistance device utilizing the TMR effect is improved. Also, the Neel effect of the magnetic resistance device utilizing the TMR effect is restrained. The magnetic resistance device includes a first ferromagnetic layer formed of ferromagnetic material, a non-magnetic insulative tunnel barrier layer coupled to the first ferromagnetic layer, a second ferromagnetic layer formed of ferromagnetic material and coupled to the tunnel barrier layer, and an anti-ferromagnetic layer formed of anti-ferromagnetic material. The second ferromagnetic layer is provided between the tunnel barrier layer and the anti-ferromagnetic layer. A perpendicular line from an optional position of the surface of the second ferromagnetic layer passes through at least two of the crystal grains of the second ferromagnetic layer.

TECHNICAL FIELD

The present invention relates to a magnetic resistance device, and moreparticularly, the present invention relates to a magnetic resistancedevice with heat resistance improved.

BACKGROUND ART

A development is carried forward to apply a magnetic resistance deviceshowing a tunnel magnetic resistance effect (TMR effect) to a magneticrandom access memory (MRAM) and a reproduction magnetic head of a highdensity magnetic recording apparatus. The TMR effect is a kind ofmagneto-resistance effect. As the magneto-resistance effect, a giantmagnetic resistance effect (GMR effect) is known in addition to the TMReffect. However, the TMR effect which shows the magneto-resistanceeffect larger than the giant magnetic resistance effect (GMR effect) ispreferable in application to MRAM and the reproduction magnetic head.

As shown in FIG. 1, the magnetic resistance device showing the TMReffect is typically composed of an anti-ferromagnetic layer 101, apinned ferromagnetic layer 102, a tunnel barrier layer 103 and a freeferromagnetic layer 104. For example, the anti-ferromagnetic layer 101is formed of anti-ferromagnetic material such as Fe—Mn and Ir—Mn. Forexample, the pinned ferromagnetic material 102 and the freeferromagnetic layer 104 are formed of ferromagnetic material such aspermalloy and have spontaneous magnetizations, respectively. Thedirection of the spontaneous magnetization of the pinned ferromagneticmaterial 102 is fixed through an exchange coupling operation receivedfrom the anti-ferromagnetic layer 101. A direction of the spontaneousmagnetization of the free ferromagnetic layer 104 is reversible into adirection parallel or anti-parallel to that of the spontaneousmagnetization of the pinned ferromagnetic material 102. The tunnelbarrier layer 103 is formed of non-magnetic substance which is aninsulator like alumina (Al₂O₃). The thickness of the tunnel barrierlayer 103 is thin to the extent that tunnel current flows in thedirection perpendicular to the surface of tunnel barrier layer 103 andtypically is 1 to 3 nm. The magnetic resistance device having such astructure is sometimes called a magnetic tunnel junction (MTJ). Thestructure of the magnetic resistance device is disclosed in JapaneseLaid Open Patent Application (JP-A-Heisei 4-103014), and U.S. Pat. No.5,650,958.

The resistance of the magnetic resistance device changes due to the TMReffect in accordance with a relative relation of direction of thespontaneous magnetization of the pinned ferromagnetic layer 102 and thatof the spontaneous magnetization of the free ferromagnetic layer 104. Inan MRAM which contains magnetic resistance devices, the change of theresistance of the magnetic resistance device is used for the detectionof stored non-volatile data. In the magnetic head which contains themagnetic resistance device, the change of the resistance of the magneticresistance device is used for the detection of an external magneticfield.

A technique to improve the characteristic of the magnetic resistancedevice showing the TMR effect is disclosed in U.S. Pat. No. 5,966,012.In the magnetic resistance device showing the TMR effect, it isimportant to decrease the magnetostatic interaction between theferromagnetic layers. The above U.S. Pat. No. 5,966,012 discloses thetechnique, in which each of a pinned ferromagnetic layer and a freeferromagnetic layer contains two ferromagnetic layers and a non-magneticlayer interposed between the ferromagnetic layers. Such a structureeffectively decreases the magnetostatic interaction between theferromagnetic layers. It is described in the U.S. Pat. No. 5,966,012 touse a Ru layer as the non-magnetic layer.

A problem of the magnetic resistance device utilizing the TMR effect isheat resistance. A method of manufacturing the MRAM and the magnetichead contain a heat-treatment process. For example, the method ofmanufacturing the MRAM contains processes in which the magneticresistance device is heated to a temperature in a range of 300° C. to400° C., such as a process of forming an interlayer insulating film, ahydrogen sintering process of a transistor, and a packaging process.When a high temperature is applied to the magnetic resistance device,the material of the anti-ferromagnetic layer 101 diffuses into thetunnel barrier layer 103 and the free ferromagnetic layer 104 throughthe pinned ferromagnetic layer 102, to degrade the characteristic of themagnetic resistance device. Especially, when the anti-ferromagneticlayer 101 is formed of the anti-ferromagnetic material which containsmanganese like Ir—Mn and Pt—Mn, the problem of the degradation of themagnetic resistance device is more important. Manganese has the natureeasy to diffuse, and it is confirmed by a composition analysis and asection observation that manganese possibly reaches the tunnel barrierlayer 103 and the free ferromagnetic layer 104 from theanti-ferromagnetic layer 101 in a short time.

A structure of the magnetic resistance device to effectively restrainthe diffusion of Mn contained in the anti-ferromagnetic layer isdisclosed in Japanese Laid Open Patent Application (JP-P2002-158381A).The magnetic resistance device has an anti-ferromagnetic layer whichcontains Mn, a magnetization fixing layer formed on theanti-ferromagnetic layer, a tunnel barrier layer formed on themagnetization fixing layer and a magnetization free layer formed on thetunnel barrier layer. The magnetization fixing layer has a structure inwhich an insulating layer or an amorphous magnetic layer is put betweenfirst and second ferromagnetic layers.

Another problem of the magnetic resistance device utilizing the TMReffect is that magnetic field necessary to reverse the direction of thespontaneous magnetization of the free ferromagnetic layer 104 isasymmetry with respect to the direction to be reversed due to the Neeleffect (orange peel effect). The Neel effect is caused in the structureof two ferromagnetic layers and a non-magnetic layer interposed betweenthe ferromagnetic layers and it depends on the non-flatness of each ofthe two ferromagnetic layers. The Neel effect combines the twoferromagnetic layers ferromagnetically and turns the directions of thespontaneous magnetizations of the two ferromagnetic layers to the samedirection (in parallel). The Neel effect makes the magnetic fieldnecessary to turn the directions of the spontaneous magnetizations ofthe two ferromagnetic layers in the anti-parallel direction larger thanthe magnetic field necessary to turn the directions of the spontaneousmagnetizations of the two ferromagnetic layers in parallel. For thereason of the Neel effect, the magnetic field necessary to reverse thedirection of the spontaneous magnetization of the free ferromagneticlayer 104 becomes asymmetry. The magnetic resistance device utilizingthe TMR effect receives large influence of the Neel effect because thethickness of the tunnel barrier layer 103 interposed between the pinnedferromagnetic layer 102 and the free ferromagnetic layer 104 is verythin.

In conjunction with the above description, a magnetic memory device isdisclosed in Japanese Laid Open Patent Application (JP-A-Heisei11-238923). A magnetic device of this conventional example is composedof an insulating layer having a thickness through which a tunnel currentcan pass, and first and second ferromagnetic films arranged to put theinsulating layer between them. A non-magnetic film is inserted in leastone of the first and second ferromagnetic films. Or, the magnetic deviceis composed of granular magnetic films having the small ferromagneticparticles which are dispersed in a dielectric substance matrix andhaving magnetic coercive force, and a ferromagnetic film arrangedclosely to the granular magnetism film. Tunnel current flows between thegranular magnetic film and the ferromagnetic film. A non-magneticsubstance film is inserted into the ferromagnetic film. According tothis conventional example, a desired output voltage value can beobtained and the decrease of a magnetic resistance changing percentageis less even if the current value flows into the ferromagnetic tunneljunction element is increased.

Also, a magneto-resistance effect device is disclosed in Japanese LaidOpen Patent Application (JP-P2000-156530A). The magneto-resistanceeffect device of this conventional example is composed of a firstmagnetic layer, the direction of whose magnetization changes due to anexternal magnetic field, a second magnetic layer, a direction of whosemagnetization is fixed, and a non-magnetic layer provided between thefirst and second magnetic layers. The magneto-resistance effect deviceis further composed of a metal barrier layer provided adjacent to thefirst magnetic layer and an electron reflection layer provided adjacentto the metal barrier layer and containing at least one selected from thegroup consisting of oxide, nitride, carbide, fluoride, chloride, sulfiteand boride. Moreover, a metal lower layer and a crystal growth controllayer may be provided. According to this conventional example, along-term reliability is improved and an initial characteristic is alsoimproved.

Also, a magnetic recording medium is disclosed in Japanese Laid OpenPatent Application (JP-P2001-76329A). In the magnetic recording mediumof this conventional example, a lower film is formed on a non-magneticsubstrate. A magnetic film of a granular structure is formed on thelower film by a sputtering method using a target which consists of amixture of ferromagnetic material and non-magnetic material with theresistance of 10⁶ Ωcm or below, or by a dual sputtering method using atarget of a ferromagnetic material and a target of non-magnetic materialwith the resistance 10⁶ Ωcm below, and then a protection film is formedon it. According to this conventional example, the magnetic film of thegranular structure with a good smoothness is provided such that frictionwith the magnetic head is small, and the magnetic recording medium isexcellent in the durability.

Also, a magnetic head having a spin valve-type magnetic sensor isdisclosed in Japanese Laid Open Patent Application (JP-P2001-101622A).The magnetic head of this conventional example has a laminate structureof a ferromagnetic fixed layer, a non-magnetic intermediate layer, and asoft magnetic free layer. The direction of the magnetization of theferromagnetic fixed layer is fixed to a magnetic field sensed by anexchange coupling section formed directly on the whole surface with ananti-ferromagnetic film or a hard magnetic layer film. The direction ofthe magnetization of the soft magnetic free layer turns in accordancewith an external magnetic field, and the magneto-resistance effect iscaused based on change in a relative angle between the direction of themagnetization of the soft magnetic free layer and the direction of themagnetization of the ferromagnetic fixed layer. A pair of electrodes isprovided to detect the change of the resistance. The ferromagnetic fixedlayer is composed of a laminate layer of a first ferromagnetic film, anon-magnetic insertion layer and a second ferromagnetic film. The firstferromagnetic film and the second ferromagnetic film have sufficientlylarge ferromagnetic coupling to the magnetic field to be sensed throughthe non-magnetic insertion layer. The directions of the magnetizationsof the first ferromagnetic film and the second ferromagnetic film are inparallel and the first ferromagnetic film and the second ferromagneticfilm function as a substantially unitary ferromagnetic film. Accordingto this conventional example, a magnetic head is provided to have a highoutput and a good waveform symmetry in a narrow gap and a narrow track.

Also, a magneto-resistance effect device is disclosed in Japanese LaidOpen Patent Application (JP-P2002-94141A). The magneto-resistance effectdevice of this conventional example is composed of an anti-ferromagneticlayer, a fixed magnetic layer which is formed to contact theanti-ferromagnetic layer and in which the direction of its magnetizationis fixed by exchange anisotropic magnetic field with theanti-ferromagnetic layer, a free magnetic layer formed through anon-magnetic intermediate layer on the fixed magnetic layer, and a biaslayer which turns the direction of the magnetization of the freemagnetic layer to a direction intersecting with the direction of themagnetization of the fixed magnetic layer. The anti-ferromagnetic layerand the fixed magnetic which is formed in contact with theanti-ferromagnetic layer are formed of an exchange coupling film. Theanti-ferromagnetic layer and the ferromagnetic layer are formed incontact with each other and a exchange coupling magnetic field isgenerated in the interface between the anti-ferromagnetic layer and theferromagnetic layer to fix the direction of the magnetization of theferromagnetic layer a predetermined direction. The anti-ferromagneticlayer is formed of anti-ferromagnetic material which contains an elementX (here, X is one or more of Pt, Pd, Ir, Rh, Ru, and Os) and Mn. Crystalgrains appear in the section of the anti-ferromagnetic layer in thedirection of the film thickness of the exchange coupling film and thecrystal grains formed in the ferromagnetic layer are discrete in atleast a part in the interface. According to this conventional example,even if a film of PtMn alloy which is the anti-ferromagnetic materialexcellent in corrosion resistance is used as the anti-ferromagneticlayer, the exchange coupling magnetic field can be made small inaccordance with the state of the crystal grain boundaries.

DISCLOSURE OF INVENTION

An object of the present invention is to improve heat resistance of amagnetic resistance device utilizing the TMR effect.

Another object of the present invention is to restrain the Neel effectof a magnetic resistance device utilizing the TMR effect and to make areverse magnetic field necessary to reverse spontaneous magnetizationsymmetrical.

In the first aspect of the present invention, a magnetic resistancedevice includes a first ferromagnetic layer formed of ferromagneticmaterial; a non-magnetic insulative tunnel barrier layer coupled to thefirst ferromagnetic layer; a second ferromagnetic layer coupled to thetunnel barrier layer and formed of ferromagnetic material; and ananti-ferromagnetic layer formed of anti-ferromagnetic material. Thesecond ferromagnetic layer is provided between the tunnel barrier layerand the anti-ferromagnetic layer. At least a part of the secondferromagnetic layer is formed such that a line perpendicular to asurface of the second ferromagnetic layer on a side of theanti-ferromagnetic layer passes through at least two of crystal grainsof the second ferromagnetic layer. By such a structure, it can beavoided that the grain boundary in the second ferromagnetic layerstraightly passes though the second ferromagnetic layer, and diffusionof the material of the anti-ferromagnetic layer to the tunnel barrierlayer can be restrained.

In order to further restrain the diffusion of the material of theanti-ferromagnetic layer to the tunnel barrier layer, it is preferablethat a line perpendicular to a surface of the second ferromagnetic layerat an optional position on the surface of the second ferromagnetic layeron a side of the anti-ferromagnetic layer passes through at least two ofcrystal grains of the second ferromagnetic layer.

When the tunnel barrier layer is formed on the side opposite to asubstrate on which the first ferromagnetic layer, the tunnel barrierlayer, the second ferromagnetic layer and the anti-ferromagnetic layerare formed, that is, when the tunnel barrier layer is formed on thesecond ferromagnetic layer, the above-mentioned structure is preferablein that the first ferromagnetic layer, the tunnel barrier layer and thesecond ferromagnetic layer are flattened and the Neel effect isrestrained.

Moreover, the magnetic resistance device may include a non-magneticlayer and a third ferromagnetic layer formed of ferromagnetic material.When the third ferromagnetic layer is formed on the anti-ferromagneticlayer, the non-magnetic layer is formed on the third ferromagneticlayer, and the second ferromagnetic layer is formed on the non-magneticlayer, the non-magnetic layer is preferably to have a function tominiature the crystal grains in the second ferromagnetic layer when thesecond ferromagnetic layer is formed.

It is possible to achieve by forming the non-magnetic layer and thesecond ferromagnetic layer of materials which belong to different pointgroups.

The concerned magnetic resistance device may include the non-magneticlayer coupled to the second ferromagnetic layer and the thirdferromagnetic layer formed of ferromagnetic material and moreover iscoupled to the non-magnetic layer. When the second ferromagnetic layer,the non-magnetic layer and the third ferromagnetic layer are situatedbetween the tunnel barrier layer and the anti-ferromagnetic layer, thenon-magnetic layer is preferably formed of an element selected from agroup consisting of Ta, Al, Mg, Ti, Mo and W or an alloy of a pluralityof elements selected from the group. The non-magnetic layer formed of anelement selected from a group consisting of Ta, Al, Mg, Ti, Mo and W oran alloy of a plurality of elements selected from the group caneffectively restrain the diffusion of the material of theanti-ferromagnetic layer, especially, Mn into the tunnel barrier layer.

In this case, it is preferable that the third ferromagnetic layer isformed on the anti-ferromagnetic layer, the non-magnetic layer is formedon the third ferromagnetic layer, and the second ferromagnetic layer isformed on the non-magnetic layer. It realizes a structure in whichcrystal grains of the second ferromagnetic layer are made small and inwhich a perpendicular line to the surface of the second ferromagneticlayer at an optional position of the surface of the second ferromagneticlayer passes through at least two of the crystal grains of the secondferromagnetic layer that the second ferromagnetic layer is formed on thenon-magnetic layer of the above-mentioned material.

It is preferable that an average grain diameter of the secondferromagnetic layer is equal to or less than ⅔ of the film thickness ofthe second ferromagnetic layer, and it is more preferable that theaverage grain diameter of the second ferromagnetic layer is equal to orless than ½ of the film thickness of the second ferromagnetic layer.

The structure of the above-mentioned magnetic resistance device ispreferable especially when the anti-ferromagnetic layer contains Mn.

In another aspect of the present invention, a magnetic resistance deviceincludes a first ferromagnetic layer formed of ferromagnetic material; anon-magnetic insulative tunnel barrier layer coupled to the firstferromagnetic layer; a second ferromagnetic layer formed offerromagnetic material and coupled to the tunnel barrier layer; and ananti-ferromagnetic layer formed of anti-ferromagnetic materialcontaining Mn. The second ferromagnetic layer is provided between thetunnel barrier layer and the anti-ferromagnetic layer, and crystalgrains in the second ferromagnetic layer are arranged to preventdiffusion of the Mn from the anti-ferromagnetic layer to the tunnelbarrier layer. Crystal grains of the second ferromagnetic layer arearranged to prevent the diffusion of Mn from the anti-ferromagneticlayer to the tunnel barrier layer.

A method of manufacturing a magnetic resistance device of the presentinvention includes (A) forming an anti-ferromagnetic layer on a surfaceof a substrate in a vacuum chamber; (B) introducing an oxidizing gasinto the vacuum chamber after forming of the anti-ferromagnetic layer;(C) exhausting the oxidizing gas from the vacuum chamber; (D) forming apinned ferromagnetic layer on the anti-ferromagnetic layer after theoxidizing gas is exhausted; (E) forming a tunnel barrier layer on thefirst ferromagnetic layer; and (F) forming a second ferromagnetic layeron the tunnel barrier layer. The introduction of the oxidizing gas intothe vacuum chamber after forming of the anti-ferromagnetic layer makesoxygen to be adhered to the surface of the anti-ferromagnetic layer. Theadhered oxygen obstructs the growth of crystal grains in the pinnedferromagnetic layer to miniature the crystal grain of the pinnedferromagnetic layer. Through the miniaturization of the crystal grainsin the pinned ferromagnetic layer, it is avoided that the grainboundaries of the pinned ferromagnetic layer straightly passes throughthe pinned ferromagnetic layer and the diffusion of the material of theanti-ferromagnetic layer to the tunnel barrier layer is restrained.

When the oxidizing gas is an oxygen gas, a partial pressure of theoxidizing gas is larger than 0 and is smaller than 1×10−4 Pa, when theoxidizing gas is introduced in the (B) step.

The method of manufacturing a magnetic resistance device of the presentinvention includes (G) forming an anti-ferromagnetic layer on a surfaceof a substrate; (H) forming a pinned ferromagnetic layer on theanti-ferromagnetic layer in an atmosphere containing an oxidizing gas;(I) forming a tunnel barrier layer on the pinned ferromagnetic layer;and (J) forming a free ferromagnetic layer on the tunnel barrier layer.A partial pressure of the oxidizing gas during the (H) process isdetermined such that the first ferromagnetic layer indicates electricconductivity. By forming the pinned ferromagnetic layer on theanti-ferromagnetic layer in the atmosphere containing an oxidizing gas,the growth of crystal grains in the pinned ferromagnetic layer isobstructed and the crystal grains in the pinned ferromagnetic layer aremade small. Through the miniaturization of the crystal grains in thepinned ferromagnetic layer, it is avoided that the grain boundaries ofthe pinned ferromagnetic layer straightly passes through the pinnedferromagnetic layer and the diffusion of the material of theanti-ferromagnetic layer to the tunnel barrier layer is restrained.

When the oxidizing gas is an oxygen gas, the partial pressure of theoxidizing gas during the (H) process is larger than 0 and is smallerthan 5×10⁻⁵ Pa.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a cross sectional view showing a conventional magneticresistance device;

FIG. 2 is cross sectional view showing a magnetic resistance deviceaccording to a first embodiment of the present invention;

FIG. 3 is an expanded view showing a pinned ferromagnetic layer of themagnetic resistance device in the first embodiment;

FIG. 4 is a diagram showing X-ray diffraction strength of the pinnedferromagnetic layer in an experiment example 1 of the present inventionand a comparison example 1;

FIG. 5 is a cross sectional view showing a magnetic resistance deviceaccording to a second embodiment of the present invention;

FIG. 6 is a table showing the material and thickness of non-magneticlayer in experiment examples 3 to 12 in the present invention;

FIG. 7 is a diagram showing an average grain diameter of a second pinnedferromagnetic layer of the magnetic resistance device in the experimentexample 3 to 12;

FIG. 8 is a diagram showing a quantity of Mn in the interface betweenthe second pinned ferromagnetic layer and a tunnel barrier layer in themagnetic resistance device in the experiment examples 3 to 12;

FIG. 9 is a diagram showing a MR ratio after heat-treatment (annealing)in the magnetic resistance device of the experiment examples 3 to 12;and

FIG. 10 is a diagram showing exchange bias magnetic field which isapplied to the second pinned ferromagnetic layer in the magneticresistance device of the experiment examples 3 to 12.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, a magnetic resistance device of the present invention willbe described with reference to the attached drawings.

(First Embodiment)

FIG. 2 shows a magnetic resistance device according to the firstembodiment of the present invention. In the magnetic resistance deviceof the first embodiment, memory cells of a MRAM utilizing the magneticresistance devices showing TMR effect are provided. The memory cell iscomposed of a substrate 1 and a base layer 2. The base layer 2 is formedon the substrate 1. The base layer 2 contains a seed layer 2 a formed onthe substrate 1 and an initial ferromagnetic layer 2 b formed on theseed layer 2 a. The seed layer 2 a is typically formed of tantalum andthe initial ferromagnetic layer 2 b is formed of Ni—Fe.

On the base layer 2, an anti-ferromagnetic layer 3 is formed. Forexample, the anti-ferromagnetic layer 3 is formed of anti-ferromagneticmaterial such as Ir—Mn and Pt—Mn. On the anti-ferromagnetic layer 3, apinned ferromagnetic layer 4 is formed. For example, the pinnedferromagnetic layer 4 is formed of ferromagnetic material such as Ni—Feand Co—Fe. The pinned ferromagnetic layer 4 formed of the ferromagneticmaterial has spontaneous magnetization. The direction of the spontaneousmagnetization of the pinned ferromagnetic layer 4 is fixed based oninteraction received from the anti-ferromagnetic layer 3.

On the pinned ferromagnetic layer 4, a tunnel barrier layer 5 is formed.For example, the tunnel barrier layer 5 is formed of insulativenon-magnetic material such as alumina (Al₂O₃). The tunnel barrier layer5 is thin to the extent that the tunnel current flows in the thicknessdirection. The film thickness of the tunnel barrier layer 5 is 1 to 3nm. On the tunnel barrier layer 5, a free ferromagnetic layer 6 isformed. For example, the free ferromagnetic layer 6 is formed offerromagnetic material such as Ni—Fe and Co—Fe and has spontaneousmagnetization. The direction of the spontaneous magnetization of thefree ferromagnetic layer 6 is reversible in a direction parallel oranti-parallel to the direction of the spontaneous magnetization of thepinned ferromagnetic layer 4. The memory cell of FIG. 2 stores 1-bitdata as the direction of the spontaneous magnetization of the freeferromagnetic layer 6. The resistance (that is, the resistance of thememory cell) between the pinned ferromagnetic layer 4 and the freeferromagnetic layer 6 is generated based on the TMR effect and changesin accordance with the direction of the spontaneous magnetization of thefree ferromagnetic layer 6. Through the change of the resistance, it ispossible to distinguish the data stored in the memory cell.

On the free ferromagnetic layer 6, a surface protection layer 7 isformed. The surface protection layer 7 is typically formed of tantalum.The surface protection layer 7 is used as an electrode connected withthe outside of the memory cell.

The crystal grains of the pinned ferromagnetic layer 4 is made fine toprevent that material contained in the anti-ferromagnetic layer 3diffuses into the tunnel barrier layer 5. As shown in FIG. 3, at least apart of the pinned ferromagnetic layer 4 is formed such that a lineperpendicular to the surface 4 a of the pinned ferromagnetic layer 4passes through at least two of the crystal grains of the pinnedferromagnetic layer 4 for the reason of the miniaturization of thecrystal grains of the pinned ferromagnetic layer 4. In this way, it canbe avoided that the grain boundary of the pinned ferromagnetic layer 4passes through the pinned ferromagnetic layer 4 in a straight. Thediffusion of material into a thin film is often carried out by grainboundary diffusion through the grain boundary of the thin film. Thestructure that the grain boundary in the pinned ferromagnetic layer 4does not pass through the pinned ferromagnetic layer 4 in straight makesthe diffusion path of material long to effectively restrain the grainboundary diffusion. In order to restrain diffusion of the materialcontained in the anti-ferromagnetic layer 3 into the tunnel barrierlayer 5 more effectively, it is preferable that the pinned ferromagneticlayer 4 is formed such that the perpendicular line to the surface 4 a ofthe pinned ferromagnetic layer 4 passes through at least two of thecrystal grains of the pinned ferromagnetic layer 4.

In order to further restrain the diffusion of the material contained inthe anti-ferromagnetic layer 3 into the tunnel barrier layer 5, it ispreferable that an average grain diameter of the crystal grains of thepinned ferromagnetic layer 4 is equal to or less than ⅔ of the filmthickness of the pinned ferromagnetic layer 4, and more preferably, isequal to or less than ½ of the film thickness of the pinnedferromagnetic layer 4.

The miniaturization of the crystal grains of the pinned ferromagneticlayer 4 is effective in the point of the restraint of the Neel effect(orange peel effect). Because the crystal grains of the pinnedferromagnetic layer 4 are made small, the pinned ferromagnetic layer 4is flattened. Therefore, the tunnel barrier layer 5 and the freeferromagnetic layer 6 are flattened. The flattening of the pinnedferromagnetic layer 4 and the free ferromagnetic layer 6 prevents amagnetic pole from being generated in the interface between theferromagnetic layer and the tunnel barrier layer 5, and restrains theNeel effect between the pinned ferromagnetic layer 4 and the freeferromagnetic layer 6 effectively. Through the restraint of the Neeleffect, an offset of a magnetic field necessary to reverse the directionof the spontaneous magnetization of the free ferromagnetic layer 6 isrestrained.

The miniaturization of the grain diameters of crystal grains of thepinned ferromagnetic layer 4 is possible by manufacturing a magneticresistance device by using either of the following two manufacturingmethods. That is, in the first manufacturing method of the magneticresistance device, the seed layer 2 a, the initial ferromagnetic layer 2b and the anti-ferromagnetic layer 3 are formed on the substrate 1 inthis order. The film formations of the seed layer 2 a, the initialferromagnetic layer 2 b and the anti-ferromagnetic layer 3 are carriedout in a vacuum chamber by using a sputtering method or a depositionmethod. After forming of the anti-ferromagnetic layer 3, an oxidizinggas of a small amount is introduced into the vacuum chamber that thefilm formation of the anti-ferromagnetic layer 3 has been carried out,and the anti-ferromagnetic layer 3 is exposed by the oxidationatmosphere. Oxygen gas is typically used as oxidizing gas. Through theexposure of the anti-ferromagnetic layer 3 to the oxidation atmosphere,the oxygen contained in the oxidizing gas is absorbed on the surface ofthe anti-ferromagnetic layer 3. Subsequently, after the vacuum chamberis vacuumed to a high vacuum, the pinned ferromagnetic layer 4 is formedon the anti-ferromagnetic layer 3. The oxygen absorbed on the surface ofthe anti-ferromagnetic layer 3 restrains the growth of crystal grains inthe pinned ferromagnetic layer 4 and makes each crystal grain small.Subsequently, on the pinned ferromagnetic layer 4, the tunnel barrierlayer 5, the free ferromagnetic layer 6 and the surface protection layer7 are formed by a well known method to a person in the art, and theforming of the magnetic resistance device completes. When oxygen gas isused as the above-mentioned oxidizing gas, a partial pressure of theoxygen gas introduced into the vacuum chamber is preferably equal to orless than 1×10⁻⁴ Pa. When the partial pressure of introduced oxygen gasis too high, the pinned ferromagnetic layer 4 is oxidized and the MRratio of the magnetic resistance device degrades.

In the second manufacturing method of the magnetic resistance devicewhich miniatures the grain diameter of crystal grains in the pinnedferromagnetic layer 4, the forming of the pinned ferromagnetic layer 4is carried out in the atmosphere which slightly contains the oxidizinggas. Specifically, in the second manufacturing method of the magneticresistance device, like the first manufacturing method of the magneticresistance device, the seed layer 2 a, the initial ferromagnetic layer 2b and the anti-ferromagnetic layer 3 are formed in this order on thesubstrate 1. Subsequently, in the atmosphere slightly containing theoxidizing gas, the pinned ferromagnetic layer 4 is formed by asputtering method or the deposition method. A slight quantity of oxygencontained in the oxidizing gas is taken into the pinned ferromagneticlayer 4. The slight quantity of oxygen taken into the pinnedferromagnetic layer 4 restrains the growth of crystal grains in thepinned ferromagnetic layer 4 and makes the crystal grains small. Afterthe forming of the pinned ferromagnetic layer 4, the tunnel barrierlayer 5, the free ferromagnetic layer 6 and the surface protection layer7 are formed on the pinned ferromagnetic layer 4 by a well known to aperson in the art, and the forming of the magnetic resistance devicecompletes. When the oxygen gas is used as the above-mentioned oxidizinggas, a partial pressure of oxygen gas in the film forming of the pinnedferromagnetic layer 4 is desirably equal to or less than 5×10⁻⁵ Pa. Whenthe partial pressure of the introduced oxygen gas is too high, thepinned ferromagnetic layer 4 is oxidized and the MR ratio of themagnetic resistance device degrades. The partial pressure of oxygen gashas been determined in such a way that the pinned ferromagnetic layer 4is conductive.

The miniaturization of the crystal grains of the pinned ferromagneticlayer 4 by the above methods is suitable in the point that it is notrequired that the pinned ferromagnetic layer 4 is a multi-layer, inorder to prevent the diffusion of the material of the anti-ferromagneticlayer 3. In the technique disclosed in the above-mentioned Japanese LaidOpen Patent Application (JP-P2002-158381A), an insulating layer or anamorphous magnetic layer is formed between two ferromagnetic layerswhich act as the pinned ferromagnetic layer. The multi-layer structureof the pinned ferromagnetic layer makes the film thickness of the wholepinned ferromagnetic layer thick. It is generally difficult to processthe ferromagnetic material, and it is not desirable that the filmthickness of the whole pinned ferromagnetic layer is thick. Also, in theMTJ, because the current flows in a direction perpendicular to the filmsurface, it is not desirable that the insulating layer exists in thepinned ferromagnetic layer.

The structure of the magnetic resistance device and the magneticresistance device manufacturing method in the above-mentioned embodimentare suitable especially when the anti-ferromagnetic layer 3 is formed ofmaterial containing manganese such as Ir—Mn and Pt—Mn. Manganese is easyto diffuse through a heat-treatment process. By reducing the graindiameters of crystal grains in the pinned ferromagnetic layer 4 formedon the anti-ferromagnetic layer 3 which contains manganese, diffusion ofmanganese into the tunnel barrier layer 5 is effectively prevented.

In this embodiment, the positions of the anti-ferromagnetic layer 3 andthe pinned ferromagnetic layer 4 are interchangeable with the positionof the free ferromagnetic layer 6. That is, the free ferromagnetic layer6 may be formed on the initial ferromagnetic layer 2 b. The tunnelbarrier layer 5 may be formed on the free ferromagnetic layer 6, and thepinned ferromagnetic layer 4 may be formed on the tunnel barrier layer6. The anti-ferromagnetic layer 3 may be formed on the pinnedferromagnetic layer 4. In this case, the pinned ferromagnetic layer 4,the tunnel barrier layer 5 and the free ferromagnetic layer 6 are notflattened. Therefore, the effect of the restraint of the Neel effect isnot achieved. However, in the structure, it is possible to effectivelyrestrain the diffusion of the material of the anti-ferromagnetic layer3.

EXPERIMENT EXAMPLES

Experiment examples 1 and 2 as the magnetic resistance device accordingto the present invention were compared with a comparison example 1. Inall of the experiment example 1, the experiment example 2 and thecomparison example 1, the seed layer 2 a was formed as a tantalum layerhaving the thickness of 3 nm. The initial ferromagnetic layer 2 b wasformed as a NiFe layer having the thickness of 3 nm, and theanti-ferromagnetic layer 3 was formed as an IrMn layer having thethickness of 10 nm. Also, the pinned ferromagnetic layer 4 was formed asa CoFe layer having the thickness of 10 nm, and the tunnel barrier layer5 was formed as an AlOx layer having the thickness of 1.5 nm. The freeferromagnetic layer 6 was formed as a NiFe layer having the thickness of5 nm, and the surface protection layer 7 was formed as a Ta layer havingthe thickness of 5 nm.

The magnetic resistance device of the experiment example 1 was formed bythe first manufacturing method of the above-mentioned magneticresistance device. After the base layer 2 and the anti-ferromagneticlayer 3 were formed in order by the sputtering method, oxygen gas wasintroduced as the oxidizing gas by a small amount in a vacuum chamberwhere the anti-ferromagnetic layer 3 had been formed. A partial pressureof oxygen gas was 5×10⁻⁵ Pa. After introduction of the oxygen gas, thevacuum chamber was vacuumed to a high vacuum and the CoFe layer for thepinned ferromagnetic layer 4 was formed on the anti-ferromagnetic layer3 by the sputtering method. Subsequently, after an Al film with thethickness of 1.5 nm was formed of the sputtering method, the Al film wasoxidized in the oxygen plasma and the AlOx layer for the tunnel barrierlayer 5 was formed. Subsequently, the free ferromagnetic layer 6 and thesurface protection layer 7 were formed in the order by the sputteringmethod.

The magnetic resistance device of the experiment example 2 was formed bythe second manufacturing method of the above-mentioned magneticresistance device. After the Ta layer, the NiFe layer and the IrMn layerwere formed in order by the sputtering method, a CoFe layer for thepinned ferromagnetic layer 4 was formed by the sputtering method in theatmosphere which contains oxygen gas of a small quantity. A partialpressure of the oxygen gas during the formation of the CoFe layer is1×10⁻⁵ Pa. Subsequently, an AlOx layer, a NiFe layer and a Ta layer wereformed in order by the same process as in the magnetic resistance deviceof the experiment example 1.

The magnetic resistance device of the comparison example 1 was formedwithout carrying out the aggressive miniaturization of the pinnedferromagnetic layer 4. After a Ta layer, a NiFe layer and an IrMn layerwere formed by the sputtering method in order, a CoFe layer was formedwithout being exposed to the atmosphere which contains oxygen gas andwithout oxygen gas introduced during the film formation. After that, theformation of an AlOx layer, a NiFe layer and a Ta layer was carried outin the order by the same process as in the magnetic resistance device ofthe experiment example 1.

FIG. 4 is a graph showing X-ray diffraction strength of the CoFe layerwhich was measured by the θ−2θ method about the experiment example 1 andthe comparison example 1. The CoFe layer of the magnetic resistancedevice of the experiment example 1 is lower in the diffraction peakintensity and wider in the peak width at half height than those of theCoFe layer of the magnetic resistance device of the comparisonexample 1. This means that the grain diameter of crystal grain in theCoFe layer of the magnetic resistance device of the experiment example 1is smaller than the comparison example 1.

An average grain diameter in the CoFe layer of the magnetic resistancedevice is calculated the following equation (1):T=0.9λ/Bcos θ  (1)where B is the peak width at half height in the diffraction peak, λ isthe wavelength (0.1541 m) of the X-ray used for the measurement and θ isan X-ray incident angle.

The average grain diameters of grains in the CoFe layer of the magneticresistance devices of the experiment example 1, the experiment example 2and the comparison example 1 which are calculated by using the aboveequation (1) are 5.0 nm, 5.0 nm and 9.1 nm, respectively. This resultshows that a plurality of crystal grains exist in the direction of thefilm thickness in the CoFe layer of the magnetic resistance device ofthe experiment example 1 and the experiment example 2 while only onecrystal grain exists in the direction of the film thickness in the CoFelayer of the magnetic resistance device of the comparison example 1.

Annealing of 400° C. for one hour was carried out to the magneticresistance devices of the experiment example 1, the experiment example 2and the comparison example 1. After the annealing, the concentrations ofMn in the interface between the CoFe layer and the AlOx layer werecompared using Auger electron spectroscopy (AES) method. In thecomparison of the Mn concentrations, the peak intensity of Mn wascorrected by using the peak values of Al and Co. When normalization wascarried out by setting the Mn concentration of the comparison example 1to one, the Mn concentrations of the experiment example 1 and theexperiment example 2 were 0.2. This result shows that the diffusion ofMn is effectively restrained in the magnetic resistance device of theexperiment example 1 and the experiment example 2.

In the magnetic resistance devices of the experiment example 1 and theexperiment example 2, the decrease in the MR ratio by the annealing wasrestrained through the restraint of the diffusion of Mn. The MR ratiosof the magnetic resistance devices of the experiment example 1, theexperiment example 2 and the comparison example 1 before the annealingwere 35%, 34.5% and 34.8%, respectively and were almost same. The MRratios in the experiment example 1, the experiment example 2 and thecomparison example 1 after the annealing at 400° C. for one hour were21%, 19% and 3%, respectively. There were little decreases of the MRratios in the magnetic resistance devices of the experiment example 1and experiment example 2.

The effect of the miniaturization of crystal grains in the CoFe layerappeared as the restraint of the offset of the magnetic field necessaryto reverse the direction of the spontaneous magnetization of the freeferromagnetic layer 6. The offset magnetic fields were 4.4 (Oe) in themagnetic resistance devices of the experiment example 1 and theexperiment example 2, respectively, while the offset magnetic field was11.30 (Oe) in the magnetic resistance device of the comparisonexample 1. It could be considered that this shows that the AlOx layerformed on the CoFe layer is flattened through the miniaturization ofcrystal grains in the CoFe layer in the experiment example 1 and theexperiment example 2 so that the Neel effect is restrained.

(Second Embodiment)

FIG. 5 shows a magnetic resistance device according to the secondembodiment of the present invention. In the second embodiment, diffusionof the material of the anti-ferromagnetic layer 3 into the tunnelbarrier layer 5 is prevented by a different method from that of thefirst embodiment.

First, in the magnetic resistance device of the second embodiment, thepinned ferromagnetic layer 11, the non-magnetic layer 12 and the secondpinned ferromagnetic layer 13 are formed on the anti-ferromagnetic layer3 in order. The tunnel barrier layer 5 is formed on the second pinnedferromagnetic layer 13. For example, the first pinned ferromagneticlayer 11 is formed of the ferromagnetic material such as Ni—Fe andCo—Fe. The first pinned ferromagnetic layer 11 formed of theferromagnetic material has the spontaneous magnetization. The directionof the spontaneous magnetization of the first pinned ferromagnetic layer11 is fixed through the interaction with the anti-ferromagnetic layer 3.

The non-magnetic layer 12 is formed of one selected from the groupconsisting of Al, Ta, Mg, Ti, Mo, and W or alloy of some of them. Thenon-magnetic layer 12 formed of such material is a non-magneticconductor.

The second pinned ferromagnetic layer 13 is formed of the ferromagneticmaterial such as Ni—Fe and Co—Fe, like the first pinned ferromagneticlayer 11. The second pinned ferromagnetic layer 13 formed of theferromagnetic material has the spontaneous magnetization. The directionof the spontaneous magnetization of the second pinned ferromagneticlayer 13 is fixed through the interaction with the first pinnedferromagnetic layer 11. Because the non-magnetic layer 12 is formed ofone selected from the group consisting of Al, Ta, Mg, Ti, Mo and W oralloy of some of them, the exchange coupling between the first pinnedferromagnetic layer 11 and the second pinned ferromagnetic layer 13 isferromagnetic. Therefore, the spontaneous magnetizations of the firstpinned ferromagnetic layer 11 and the second pinned ferromagnetic layer13 turn to the same direction. The process in which the spontaneousmagnetizations of the first pinned ferromagnetic layer 11 and secondpinned ferromagnetic layer 13 are turned to desired directions iscarried out through the application of the external magnetic field. Inthis case, it is suitable in the point that a strong magnetic field isnot needed in the process which the spontaneous magnetization are turnedto the desired directions that the directions of the spontaneousmagnetization of the first pinned ferromagnetic layer 11 and the secondpinned ferromagnetic layer 13 are same.

The resistance between the free ferromagnetic layer 6 and the secondpinned ferromagnetic layer 13 (i.e., the resistance of the memory cell)changes in accordance with the direction of the spontaneousmagnetization of the free ferromagnetic layer 6 through the TMR effect.Through the change of the resistance, it is possible to distinguish thedata stored in the memory cell.

The non-magnetic layer 12 is formed of one selected from the groupconsisting of Al, Ta, Mg, Ti, Mo and W or alloy of some of them, andminiatures crystal grains in the second pinned ferromagnetic layer 13formed on the non-magnetic layer 12. Like the pinned ferromagnetic layer4 of the first embodiment, at least a part of the second pinnedferromagnetic layer 13 is formed through the miniaturization of crystalgrains in the second pinned ferromagnetic layer 13 in such a way that aline perpendicular to the surface of the second pinned ferromagneticlayer 13 passes through at least two of the crystal grains of the secondpinned ferromagnetic layer 13. Thus, it can be avoided for the grainboundary in the second pinned ferromagnetic layer 13 to pass through thepinned ferromagnetic layer 4 in straight, and the diffusion the materialcontained in the anti-ferromagnetic layer 3, especially Mn into thetunnel barrier layer 5 can be restrained. In order to restrain thediffusion of the material contained in the anti-ferromagnetic layer 3into the tunnel barrier layer 5 more effectively, it is desirable thatthe second pinned ferromagnetic layer 13 is formed in such a way thatthe line perpendicular to the surface of the second pinned ferromagneticlayer 13 from an optional position of the surface thereof passes throughat least two of the crystal grains of the second pinned ferromagneticlayer 13.

The mechanism of the miniaturization of crystal grains in the secondpinned ferromagnetic layer 13 due to the non-magnetic layer 12 is notclear. The inventor estimates that the mechanism relates to thehindering of the growth of large crystal grain because the non-magneticlayer 12 formed of the above-mentioned material and the second pinnedferromagnetic layer 13 formed of the ferromagnetic material belong todifferent point groups and/or those lattice constants are different.

The miniaturization of crystals grains in the second pinnedferromagnetic layer 13 flattens the second pinned ferromagnetic layer13, the tunnel barrier layer 5 and the free ferromagnetic layer 6 andrestrains the Neel effect effectively, like the first embodiment. Asmentioned above, the restraint of the Neel effect is effective in thepoint that the offset of the reverse magnetic field of the freeferromagnetic layer 6 can be reduced.

It is preferable in the point that the function to prevent the diffusionof Mn is given to the non-magnetic layer 12 itself that the non-magneticlayer 12 is formed the material selected from the group consisting ofAl, Ta, Mg, Ti, Mo and W or alloy of some of them.

In order to further restrain the diffusion of the material contained inthe anti-ferromagnetic layer 3 into the tunnel barrier layer 5, it ispreferable that the second pinned ferromagnetic layer 13 is formed insuch a way that an average grain diameter of the crystal grains of thepinned ferromagnetic layer 13 is equal to or less than ⅔ of the filmthickness of the pinned ferromagnetic layer 13. It is more preferablethat the average grain diameter is equal to or less than ½ of the filmthickness of the second pinned ferromagnetic layer 13.

EXPERIMENT EXAMPLE

The experiment examples 3 to 12 of the magnetic resistance device of thepresent invention were compared with the comparison example 1 and acomparison example 2. The structures of the experiment example 3 to 12of the magnetic resistance device and the comparison example 1 and 2 ofthe magnetic resistance device are as follows.

In the experiment examples 3 to 12, the CoFe layer having the thicknessof 2 nm was formed as the first pinned ferromagnetic layer 11 and theCoFe layer having the thickness of 10 nm was formed as the second pinnedferromagnetic layer 13.

The experiment example 3 to the experiment example 12 differ in thematerial and/or thickness of the non-magnetic layer 12 from each other.As shown in FIG. 6, the non-magnetic layers 12 in the experiment example3 to the experiment example 7 of the magnetic resistance device wereformed as the Al layer. The thicknesses of the non-magnetic layers 12 inthe experiment example 3 to the experiment example 7 were 0.3, 0.5, 0.7,1.0 and 1.5 nm, respectively. The non-magnetic layers 12 in theexperiment example 8 to the experiment example 12 of the magneticresistance device were formed as the Ta layer. The thicknesses of thenon-magnetic layers 12 in the experiment example 8 to the experimentexample 12 were 0.3, 0.5, 0.7, 1.0 and 1.5 nm, respectively.

The structure of the comparison example 1 of the magnetic resistancedevice was as described in the first embodiment. In the comparisonexample 1 of the magnetic resistance device, the CoFe layer having thethickness of 10 nm was used as the pinned ferromagnetic layer instead ofthe first pinned ferromagnetic layer 11, the non-magnetic layer 12 andthe second pinned ferromagnetic layer 13.

The comparison example 2 of the magnetic resistance device differs fromthe experiment example 3 to the experiment example 12 in the material ofthe non-magnetic layer 12. In the experiment example 3 to the experimentexample 12, the non-magnetic layers 12 were formed from the Al layer orthe Ta layer, but the non-magnetic layer 12 of the comparison example 2was formed from a Ru layer having the thickness of 1.0 nm.

The structures of the other portions of the experiment example 3 to theexperiment example 12, the comparison example 1 and the comparisonexample 2 of the magnetic resistance device were same. In all of theexperiment example 3 to the experiment example 12, the comparisonexample 1 and the comparison example 2, the seed layers 2 a were formedfrom the tantalum layer having the thickness of 3 nm, the initialferromagnetic layers 2 b were formed from the NiFe layer having thethickness of 3 nm, the anti-ferromagnetic layers 3 were formed from theIrMn layer having the thickness of 10 nm, the tunnel barrier layers 5were formed from the AlOx layer having the thickness of 1.5 nm, the freeferromagnetic layers 6 were formed from the NiFe layer having thethickness of 5 nm, and the surface protection layers 7 were formed fromthe Ta layer having the thickness of 5 nm.

FIG. 7 shows average grain diameters of crystal grains in the secondpinned ferromagnetic layers 13 of the experiment example 3 to theexperiment example 12 of the magnetic resistance device. The averagegrain diameter was calculated from the peak width at half height in theX ray diffraction peak, like the first embodiment. The average graindiameters of the experiment example 3 to the experiment example 12 ofthe magnetic resistance device were in a range of 4.5 nm to 6.0 nm. Thismeans that a plurality of crystal grains exist in the direction of thethickness in the second pinned ferromagnetic layers 13 of the experimentexample 3 to the experiment example 12.

FIG. 8 shows Mn concentration in the interface between the second pinnedferromagnetic layer 13 and the tunnel barrier layer 5 after theannealing was carried out to the magnetic resistance device at 400° C.for one hour. The Mn concentrations were normalized based on the Mnconcentration in the interface between the pinned ferromagnetic layerand the tunnel barrier layer in the comparison example 1. The Mnconcentrations were measured by AES, like the first embodiment.

As shown in FIG. 8, in the experiment example 3 to the experimentexample 12 of the magnetic resistance devices in which the non-magneticlayers 12 were formed from the Al layer or the Ta layer, diffusion of Mninto the tunnel barrier layers 5 was restrained. In the experimentexample 3 to the experiment example 12 of the magnetic resistancedevices, diffusion of Mn into the tunnel barrier layers 5 is restrainedalthough the non-magnetic layers 12 only has the thin film thickness of0.3 nm.

In the comparison example 2 in which the non-magnetic layer 12 wasformed from the Ru layer, the effect in which the diffusion of Mn intothe tunnel barrier layer 5 is restrained is slightly found. However, therestraint of the diffusion is more effective in the experiment example 3to the experiment example 12 of the magnetic resistance device, in whichthe non-magnetic layers 12 were formed from the Al layer or the Talayer. Thus, it could be considered that the crystal grains aresufficiently made small to the extent that the diffusion of Mn into thesecond pinned ferromagnetic layer 13 can be restrained in the experimentexample 3 to the experiment example 12 of the magnetic resistancedevices in which the non-magnetic layer 12 is formed from the Al layeror the Ta layer, while the effect of the miniaturization of crystalgrains in the second pinned ferromagnetic layer 13 is not sufficient inthe comparison example 2 of the magnetic resistance device in which thenon-magnetic layer 12 is formed from the Ru layer.

The dependence of the concentration of Mn diffused into the interface ofthe tunnel barrier layer 5 upon the film thickness of the non-magneticlayer 12 is small. This suggests that the miniaturization of crystalgrains in the second pinned ferromagnetic layer 13 and prevention of thediffusion in the second pinned ferromagnetic layer 13 contribute more toprevent the diffusion of Mn rather than the non-magnetic layer 12 actsas a diffusion barrier.

In the experiment example 3 to the experiment example 12 of the magneticresistance devices, the diffusion of Mn into the tunnel barrier layer 5is restrained and further the degradation of the MR ratio by theannealing is reduced. As shown in FIG. 9, the MR ratios were in a range17% to 23% in the experiment example 3 to the experiment example 12 ofthe magnetic resistance devices after the annealing at 400° C. for onehour and were more conspicuously larger than 3% of the MR ratio of thecomparison example 1 of the magnetic resistance device.

The insertion of the non-magnetic layer 12 separates theanti-ferromagnetic material 3 and the second pinned ferromagnetic layer13 and has a possibility to reduce exchange bias magnetic field H_(ex)through the exchange coupling between the anti-ferromagnetic material 3and the second pinned ferromagnetic layer 13. When the exchange biasmagnetic field H_(ex) becomes weak, the second pinned ferromagneticmaterial 13 becomes easy to reverse and therefore, the magnetic fieldrange in which the directions of the spontaneous magnetizations of thefree ferromagnetic layer 6 and the second pinned ferromagnetic layer 13are anti-parallel becomes narrow. It is qualitatively preferable thatthe exchange bias magnetic field H_(ex) is larger.

FIG. 10 shows the exchange bias magnetic field H_(ex) applied to thesecond pinned ferromagnetic layer 13 in each of the experiment example 3to the experiment example 12. In the comparison example 1, in which theanti-ferromagnetic layer was coupled directly on the pinnedferromagnetic layer, the exchange bias magnetic field H_(ex) applied tothe pinned ferromagnetic layer was about 980 (Oe). In the experimentexample 3 to the experiment example 7, in which the non-magnetic layers12 were formed from the Al layer, the degradation of the fixed force ofthe spontaneous magnetization of the second pinned ferromagnetic layer13 did not occur when approximately the same exchange bias magneticfield H_(ex) as the comparison example 1 of the magnetic resistancedevice was applied to the second pinned ferromagnetic layer 13. On theother hand, in the experiment example 8 to the experiment example 12 ofthe magnetic resistance devices, in which the non-magnetic layers 12were formed from the Ta layer, the exchange bias magnetic field H_(ex)was weakened. However, the magnitude of exchange bias magnetic fieldH_(ex) was kept to the magnitude that is sufficient in case of practicaluse, even when the non-magnetic layers 12 were formed from the Ta layer.From the viewpoint of the securing of the exchange bias magnetic fieldH_(ex), it is preferable that the non-magnetic layer 12 is formed fromthe Al layer.

In the experiment example 3 to the experiment example 12 of the magneticresistance devices, the offset of the reverse magnetic field of thespontaneous magnetization of the free ferromagnetic layer 6 isrestrained, like the first embodiment. The offset magnetic field in theexperiment example 3 to the experiment example 12 of the magneticresistance device was 5.4(Oe) at maximum, and was smaller than theoffset magnetic field (11.30 (Oe)) of the comparison example 1.

When a Mg layer, Ti layer, Mo layer or W layer having the thickness of0.7 nm were used for the non-magnetic layer 12, the Mn concentration inthe interface between the second pinned ferromagnetic layer 13 and thetunnel barrier layer 5 decreased to a half of the Mn concentration ofthe comparison example 1 and the effect of the restraint of thediffusion of Mn was accomplished. Thus, it is made clear that the Mglayer, the Ti layer, the Mo layer and the W layer are available as thenon-magnetic layer 12.

In the present invention, the heat resistance of the magnetic resistancedevice utilizing the TMR effect is improved.

Also, according to the present invention, the Neel effect of themagnetic resistance device utilizing the TMR effect is restrained and amagnetic field necessary for turning-over the spontaneous magnetizationbecomes symmetrical.

1. A magnetic resistance device comprising: a first ferromagnetic layerformed of ferromagnetic material; a non-magnetic insulative tunnelbarrier layer coupled to said first ferromagnetic layer; a secondferromagnetic layer coupled to said tunnel barrier layer and formed offerromagnetic material; and an anti-ferromagnetic layer formed ofanti-ferromagnetic material, wherein said second ferromagnetic layer isprovided between said tunnel barrier layer and said anti-ferromagneticlayer, and at least a part of said second ferromagnetic layer is formedsuch that a line perpendicular to a surface of said second ferromagneticlayer on a side of said anti-ferromagnetic layer passes through at leasttwo of crystal grains of said second ferromagnetic layer.
 2. Themagnetic resistance device according to claim 1, further comprising asubstrate, wherein said first ferromagnetic layer, said tunnel barrierlayer, said second ferromagnetic layer and said anti-ferromagnetic layerare formed above a surface of said substrate, and said tunnel barrierlayer is formed on a side opposite to said substrate with respect tosaid second ferromagnetic layer.
 3. The magnetic resistance deviceaccording to claim 1, further comprising: a non-magnetic layer; and athird ferromagnetic layer formed of ferromagnetic material, wherein saidthird ferromagnetic layer is formed on said anti-ferromagnetic layer,said non-magnetic layer is formed on said third ferromagnetic layer,said second ferromagnetic layer is formed on said non-magnetic layer,and said non-magnetic layer has a function to miniature said crystalgrains in said second ferromagnetic layer when said second ferromagneticlayer is formed.
 4. The magnetic resistance device according to claim 3,wherein said non-magnetic layer and said second ferromagnetic layer areformed of materials which belong to different point groups.
 5. Themagnetic resistance device according to claim 1, further comprising: anon-magnetic layer coupled to said second ferromagnetic layer; and athird ferromagnetic layer formed of ferromagnetic material and coupledto said non-magnetic layer, wherein said second ferromagnetic layer,said non-magnetic layer and said third ferromagnetic layer are providedbetween said tunnel barrier layer and said anti-ferromagnetic layer, andsaid non-magnetic layer is formed of an element selected from a groupconsisting of Ta, Al, Mg, Ti, Mo and W or an alloy of a plurality ofelements selected from the group.
 6. The magnetic resistance deviceaccording to claim 5, wherein said third ferromagnetic layer is formedon said anti-ferromagnetic layer, said non-magnetic layer is formed onsaid third ferromagnetic layer, and said second ferromagnetic layer isformed on said non-magnetic layer.
 7. The magnetic resistance deviceaccording to claim 1, wherein an average grain diameter of grains insaid second ferromagnetic layer is equal to or less than ⅔ of a filmthickness of said second ferromagnetic layer.
 8. The magnetic resistancedevice according to claim 7, wherein said average grain diameter of saidgrains in said second ferromagnetic layer is equal to or less than ½ ofthe film thickness of said second ferromagnetic layer.
 9. The magneticresistance device according to claim 1, wherein said anti-ferromagneticlayer contains Mn.
 10. A magnetic resistance device comprising: a firstferromagnetic layer formed of ferromagnetic material; a non-magneticinsulative tunnel barrier layer coupled to said first ferromagneticlayer; a second ferromagnetic layer formed of ferromagnetic material andcoupled to said tunnel barrier layer; and an anti-ferromagnetic layerformed of anti-ferromagnetic material containing Mn, wherein said secondferromagnetic layer is provided between said tunnel barrier layer andsaid anti-ferromagnetic layer, and crystal grains in said secondferromagnetic layer are arranged to prevent diffusion of said Mn fromsaid anti-ferromagnetic layer to said tunnel barrier layer.